Exercise and the Regulation of Hepatic Metabolism

Histological improvements following energy restriction and exercise: The role of insulin resistance in resolution of MASH

BACKGROUND & AIMS

Metabolic dysfunction-associated steatohepatitis (MASH) is one of the most common liver diseases worldwide and is characterized by multi-tissue insulin resistance. The effects of a 10-month energy restriction and exercise intervention on liver histology, anthropometrics, plasma biochemistries, and insulin sensitivity were compared to standard of care (control) to understand mechanisms that support liver health improvements.

METHODS

Following medical diagnosis of MASH, individuals were randomized to treatment (n = 16) or control (n = 8). Liver fat (magnetic resonance spectroscopy), 18-hour plasma biochemical measurements, and isotopically labeled hyperinsulinemic-euglycemic clamps were completed pre- and post-intervention. Body composition and cardiorespiratory fitness (VO2peak) were also measured mid-intervention. Those in the treatment group were counseled to reduce energy intake and completed supervised, high-intensity interval training (3x/week) for 10 months. Controls continued physician-directed care.

RESULTS

Treatment induced significant (p <0.05) reductions in body weight, fat mass, and liver injury, while VO2peak (p <0.05) and non-esterified fatty acid suppression (p = 0.06) were improved. Both groups exhibited reductions in total energy intake, hemoglobin A1c, hepatic insulin resistance, and liver fat (p <0.05). Compared to control, treatment induced a two-fold increase in peripheral insulin sensitivity which was significantly related to higher VO2peak and resolution of liver disease.

CONCLUSIONS

Exercise and energy restriction elicited significant and clinically meaningful treatment effects on liver health, potentially driven by a redistribution of excess nutrients to skeletal muscle, thereby reducing hepatic nutrient toxicity. Clinical guidelines should emphasize the addition of aerobic exercise in lifestyle treatments for the greatest histologic benefit in individuals with advanced MASH.

IMPACT AND IMPLICATIONS

The mechanisms that underpin histologic improvement in individuals with metabolic dysfunction-associated steatohepatitis (MASH) are not well understood. This study evaluated the relationship between liver and metabolic health, testing how changes in one may affect the other. We investigated the effects of energy restriction and exercise on the association between multi-tissue insulin sensitivity and histologic improvements in participants with biopsy-proven MASH. For the first time, these results show that an improvement in peripheral (but not hepatic) insulin sensitivity and systemic markers of muscle function (i.e. cardiorespiratory fitness) were strongly related to resolution of liver disease. Extrahepatic disposal of substrates and improved fitness levels supported histologic improvement, confirming the addition of exercise as crucial to lifestyle interventions in MASH.

CLINICAL TRIAL NUMBER

NCT03151798.

LCoRL Regulates Growth and Metabolism

Genome-wide association studies (GWAS) in humans and livestock have identified genes associated with metabolic traits. However, the causality of many of these genes on metabolic homeostasis is largely unclear due to a lack of detailed functional analyses. Here we report ligand-dependent corepressor-like (LCoRL) as a metabolic regulator for body weight and glucose homeostasis. Although GWAS data show that LCoRL is strongly associated with body size, glucose homeostasis, and other metabolic traits in humans and livestock, functional investigations had not been performed. We generated Lcorl knockout mice (Lcorl-/-) and characterized the metabolic traits. We found that Lcorl-/- pups are born smaller than the wild-type (WT) littermates before reaching normal weight by 7 to 9 weeks of age. While aging, Lcorl-/- mice remain lean compared to WT mice, which is associated with a decrease in daily food intake. Glucose tolerance and insulin sensitivity are improved in Lcorl-/- mice. Mechanistically, this stunted growth is linked to a reduction of circulating levels of IGF-1. The expression of the genes downstream of GH signaling and the genes involved in glucose and lipid metabolism are altered in the liver of Lcorl-/- mice. Furthermore, Lcorl-/- mice are protected against a high-fat diet challenge and show reduced exercise capacity in an exercise stress test. Collectively, our results are congruent with many of the metabolic parameters linked to the Lcorl locus as reported in GWAS in humans and livestock.

Glucose metabolism in the perfused liver did not improve with resistance training in male Swiss mice under caloric restriction

CONTEXT

Energy homeostasis is a primary factor for the survival of mammals. Many tissues and organs, among which is the liver, keep this homeostasis in varied circumstances, including caloric restriction (CR) and physical activity.

OBJECTIVE

This study investigated glucose metabolism using the following groups of eight-week-old male Swiss mice: CS, sedentary and fed freely; RS, sedentary and RT, trained, both under 30% CR (n = 20-23 per group).

RESULTS

Organs and fat depots of groups RS and RT were similar to CS, although body weight was lower. CR did not impair training performance nor affected systemic or hepatic glucose metabolism. Training combined with CR (group RT) improved in vivo glucose tolerance and did not affect liver gluconeogenesis.

CONCLUSIONS

The mice tolerated the prolonged moderate CR without impairment of their well-being, glucose homeostasis, and resistance training performance. But the higher liver gluconeogenic efficiency previously demonstrated using this training protocol in mice was not evidenced under CR.

The effect of an acute bout of exercise on circulating vitamin D metabolite concentrations: a randomised crossover study in healthy adults

The effect of acute exercise on circulating concentrations of vitamin D metabolites is unclear. To address this knowledge gap, we examined the effect of a bout of treadmill-based exercise versus rest on circulating concentrations of 25(OH)D3, 25(OH)D2, 3-epi-25(OH)D3, 24,25(OH)2D3, 1,25(OH)2D3, and vitamin D2 and D3 in healthy men and women. Thirty-three healthy adults (14 females, 41 (15) years, body mass index 26.2 (3.7) kg/m2,V ̇ O 2 max ${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}{\mathrm{max}}}}$ 36.2 (9.2) ml/kg/min; mean (SD)) completed two laboratory visits involving 60 min of moderate-intensity treadmill exercise (60%V ̇ O 2 max ${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}{\mathrm{max}}}}$ ) versus 60 min of seated rest, both in an overnight fasted-state, as part of a randomised crossover design. Venous blood samples were drawn at baseline, immediately (0 h), 1 h and 24 h after the exercise or rest-period. There was a significant time × trial interaction effect for total circulating 25(OH)D (P = 0.0148), 25(OH)D3 (P = 0.0127) and 1,25(OH)2D3 (P = 0.0226). Immediately post-exercise, 25(OH)D, 25(OH)D3 and 1,25(OH)2D3 concentrations were significantly elevated compared to the control resting condition, and 1,25(OH) 2D3 remained significantly elevated 1 h later. Circulating albumin, vitamin D binding protein, calcium and parathyroid hormone were elevated immediately post-exercise. Thus, an acute bout of moderate intensity exercise transiently increases concentrations of circulating 25(OH)D and 1,25(OH)2D3 compared to resting conditions. KEY POINTS: Observational studies suggest that acute exercise might change circulating concentrations of vitamin D metabolites, but this has not been investigated using randomised crossover studies and using robust analytical procedures. In this study, we used a randomised crossover design to examine the effect of a bout of treadmill-based exercise (vs. rest) on circulating concentrations of a wide range of vitamin D metabolites in healthy humans. We show that an acute bout of moderate intensity exercise transiently increases concentrations of circulating 25(OH)D and 1,25(OH)2D3 compared to resting conditions. These findings indicate that regular exercise could lead to transient but regular windows of enhanced vitamin D biological action.

Hepato-splanchnic fluxes during exercise in patients with cirrhosis-a pilot study

In cirrhotic patients, compromised hepatocyte function combined with disturbed hepatic blood flow could affect hepato-splanchnic substrate and metabolite fluxes and exacerbate fatigue during exercise. Eight cirrhotic patients performed incremental cycling trials (3 × 10 min; at light (28 [19-37] W; median with range), moderate (55 [41-69] W), and vigorous (76 [50-102] W) intensity). Heart rate increased from 68 (62-74) at rest to 95 (90-100), 114 (108-120), and 140 (134-146) beats/min (P < 0.05), respectively. The hepatic blood flow, as determined by constant infusion of indocyanine green with arterial and hepatic venous sampling, declined from 1.01 (0.75-1.27) to 0.69 (0.47-0.91) L/min (P < 0.05). Hepatic glucose output increased from 0.6 (0.5-0.7) to 1.5 (1.3-1.7) mmol/min, while arterial lactate increased from 0.8 (0.7-0.9) to 9.0 (8.1-9.9) mmol/L (P < 0.05) despite a rise in hepatic lactate uptake. Arterial ammonia increased in parallel to lactate from 47.3 (40.1-54.5) to 144.4 (120.5-168.3) μmol/L (P < 0.05), although hepatic ammonia uptake increased from 19.5 (12.4-26.6) to 69.5 (46.5-92.5) μmol/min (P < 0.05). Among the 14 amino acids measured, glutamate was released in the liver, while the uptake of free fatty acids decreased. During exercise at relatively low workloads, arterial lactate and ammonia levels were comparable to those seen in healthy subjects at higher workloads, while euglycemia was maintained due to sufficient hepatic glucose production. The accumulation of lactate and ammonia may contribute to exercise intolerance in patients with cirrhosis.

Postprandial exercise regulates tissue-specific triglyceride uptake through angiopoietin-like proteins

Fuel substrate switching between carbohydrates and fat is essential for maintaining metabolic homeostasis. During aerobic exercise, the predominant energy source gradually shifts from carbohydrates to fat. While it is well known that exercise mobilizes fat storage from adipose tissues, it remains largely obscure how circulating lipids are distributed tissue-specifically according to distinct energy requirements. Here, we demonstrate that aerobic exercise is linked to nutrient availability to regulate tissue-specific activities of lipoprotein lipase (LPL), the key enzyme catabolizing circulating triglyceride (TG) for tissue uptake, through the differential actions of angiopoietin-like (ANGPTL) proteins. Exercise reduced the tissue binding of ANGPTL3 protein, increasing LPL activity and TG uptake in the heart and skeletal muscle in the postprandial state specifically. Mechanistically, exercise suppressed insulin secretion, attenuating hepatic Angptl8 transcription through the PI3K/mTOR/CEBPα pathway, which is imperative for the tissue binding of its partner ANGPTL3. Constitutive expression of ANGPTL8 hampered lipid utilization and resulted in cardiac dysfunction in response to exercise. Conversely, exercise promoted the expression of ANGPTL4 in white adipose tissues, overriding the regulatory actions of ANGPTL8/ANGPTL3 in suppressing adipose LPL activity, thereby diverting circulating TG away from storage. Collectively, our findings show an overlooked bifurcated ANGPTL-LPL network that orchestrates fuel switching in response to aerobic exercise.

Molecular adaptations in response to exercise training are associated with tissue-specific transcriptomic and epigenomic signatures

Regular exercise has many physical and brain health benefits, yet the molecular mechanisms mediating exercise effects across tissues remain poorly understood. Here we analyzed 400 high-quality DNA methylation, ATAC-seq, and RNA-seq datasets from eight tissues from control and endurance exercise-trained (EET) rats. Integration of baseline datasets mapped the gene location dependence of epigenetic control features and identified differing regulatory landscapes in each tissue. The transcriptional responses to 8 weeks of EET showed little overlap across tissues and predominantly comprised tissue-type enriched genes. We identified sex differences in the transcriptomic and epigenomic changes induced by EET. However, the sex-biased gene responses were linked to shared signaling pathways. We found that many G protein-coupled receptor-encoding genes are regulated by EET, suggesting a role for these receptors in mediating the molecular adaptations to training across tissues. Our findings provide new insights into the mechanisms underlying EET-induced health benefits across organs.

Understanding the variation in exercise responses to guide personalized physical activity prescriptions

Understanding the factors that contribute to exercise response variation is the first step in achieving the goal of developing personalized exercise prescriptions. This review discusses the key molecular and other mechanistic factors, both extrinsic and intrinsic, that influence exercise responses and health outcomes. Extrinsic characteristics include the timing and dose of exercise, circadian rhythms, sleep habits, dietary interactions, and medication use, whereas intrinsic factors such as sex, age, hormonal status, race/ethnicity, and genetics are also integral. The molecular transducers of exercise (i.e., genomic/epigenomic, proteomic/post-translational, transcriptomic, metabolic/metabolomic, and lipidomic elements) are considered with respect to variability in physiological and health outcomes. Finally, this review highlights the current challenges that impede our ability to develop effective personalized exercise prescriptions. The Molecular Transducers of Physical Activity Consortium (MoTrPAC) aims to fill significant gaps in the understanding of exercise response variability, yet further investigations are needed to address additional health outcomes across all populations.

Chronic exercise improves hepatic acylcarnitine handling

Exercise mediates tissue metabolic function through direct and indirect adaptations to acylcarnitine (AC) metabolism, but the exact mechanisms are unclear. We found that circulating medium-chain acylcarnitines (AC) (C12-C16) are lower in active/endurance trained human subjects compared to sedentary controls, and this is correlated with elevated cardiorespiratory fitness and reduced adiposity. In mice, exercise reduced serum AC and increased liver AC, and this was accompanied by a marked increase in expression of genes involved in hepatic AC metabolism and mitochondrial β-oxidation. Primary hepatocytes from high-fat fed, exercise trained mice had increased basal respiration compared to hepatocytes from high-fat fed sedentary mice, which may be attributed to increased Ca2+ cycling and lipid uptake into mitochondria. The addition of specific medium- and long-chain AC to sedentary hepatocytes increased mitochondrial respiration, mirroring the exercise phenotype. These data indicate that AC redistribution is an exercise-induced mechanism to improve hepatic function and metabolism.

Effect of a moderate alcohol dose on physiological responses during rest and prolonged cycling

AIM

We examined the acute effects of a moderate alcohol dose (48 g) ingested before prolonged cycling on acute physiological responses in eight healthy males (mean ± SD; 23 ± 2 years; 1.77 ± 0.04 m; 75.8 ± 4.1 kg).

METHODS

In a randomized order, euhydrated participants completed two experimental sessions with the sequence of 150-min seated at rest, 90-min of cycling at 50% of the maximal rate of oxygen consumption ($\dot{\textrm V}\textrm O$2max), 120-min seated at rest. Participants drank 250 mL of flavored squash with or without alcohol (vodka; ~16 g) at 10, 40, and 70 min of the initial resting phase, giving a cumulative fluid intake of 750 mL with 48 g of alcohol. Heart rate, blood glucose, breath alcohol concentration, and respiratory gasses were recorded throughout the entire trial with cumulative urine volume recorded during both rest phases.

RESULTS

Total carbohydrate (control = 115 ± 19 g: alcohol = 119 ± 21 g; P = 0.303) and lipid (control = 17 ± 4 g: alcohol = 20 ± 7 g; P = 0.169) oxidation was similar between conditions. Average heart rate was 7% higher in the alcohol condition (control = 111 ± 12 bpm; alcohol = 119 ± 11 bpm; P = 0.003). Blood glucose concentrations were similar between conditions during (P = 0.782) and after exercise (P = 0.247). Urine output was initially increased between conditions following alcohol ingestion before diminishing (P < 0.001) with no difference in total cumulative urine output (P = 0.331).

CONCLUSION

Consuming an alcoholic drink containing 48 g of alcohol in the hour before moderate intensity sub-maximal aerobic exercise led to detectable increases in heart rate and rate of urine production with no effect on substrate use.

Long-term physical inactivity induces significant changes in biochemical pathways related to metabolism of proteins and glycerophospholipids in mice

Physical inactivity affects multiple organ systems, including the musculoskeletal system, which upsets the delicate balance of several secretory factors leading to metabolic derailment. This reduces contractile recruitment of the skeletal muscle with dampening of its oxidative capacity resulting in impaired intramuscular lipid metabolism and substrate utilization. We hypothesized that this altered phenotype would also have an indispensable effect on circulatory cytokines and the level of metabolic intermediates. In this study, comparison between sedentary (SED) and exercised (EXER) animal models showed that organismal metabolic parameters (body mass, oxygen utilization and glucose tolerance) are altered based on physical activity. Our data suggest that cytokines linked to glycemic excursions (insulin, c-peptide, glucagon) and their passive regulators (leptin, BDNF, active ghrelin, and GIP) exhibit changes in the SED group. Furthermore, some of the proinflammatory cytokines and myokines were upregulated in SED. Interestingly, serum metabolite analysis showed that the levels of glucogenic amino acids (alanine, glycine, tryptophan, proline and valine), nitrogenous amino acids (ornithine, asparagine, and glutamine) and myogenic metabolites (taurine, creatine) were altered due to the level of physical activity. A pyrimidine nucleoside (uridine), lipid metabolite (glycerol) and ketone bodies (acetoacetate and acetate) were found to be altered in SED. A Spearman rank correlation study between SED and CTRL showed that cytokines build a deformed network with metabolites in SED, indicating significant modifications in amino acids, phosphatidylinositol phosphate and glycerophospholipid metabolic pathways. Overall, long-term physical inactivity reorganizes the profile of proinflammatory cytokines, glucose sensing hormones, and protein and glycerophospholipid metabolism, which might be the initial factors of metabolic diseases due to SED.

Exercise training adaptations in liver glycogen and glycerolipids require hepatic AMP-activated protein kinase in mice

Regular exercise elicits adaptations in glucose and lipid metabolism that allow the body to meet energy demands of subsequent exercise bouts more effectively and mitigate metabolic diseases including fatty liver. Energy discharged during the acute exercise bouts that comprise exercise training may be a catalyst for liver adaptations. During acute exercise, liver glycogenolysis and gluconeogenesis are accelerated to supply glucose to working muscle. Lower liver energy state imposed by gluconeogenesis and related pathways activates AMP-activated protein kinase (AMPK), which conserves ATP partly by promoting lipid oxidation. This study tested the hypothesis that AMPK is necessary for liver glucose and lipid adaptations to training. Liver-specific AMPKα1α2 knockout (AMPKα1α2fl/fl+AlbCre) mice and littermate controls (AMPKα1α2fl/fl) completed sedentary and exercise training protocols. Liver nutrient fluxes were quantified at rest or during acute exercise following training. Liver metabolites and molecular regulators of metabolism were assessed. Training increased liver glycogen in AMPKα1α2fl/fl mice, but not in AMPKα1α2fl/fl+AlbCre mice. The inability to increase glycogen led to lower glycogenolysis, glucose production, and circulating glucose during acute exercise in trained AMPKα1α2fl/fl+AlbCre mice. Deletion of AMPKα1α2 attenuated training-induced declines in liver diacylglycerides. In particular, training lowered the concentration of unsaturated and elongated fatty acids comprising diacylglycerides in AMPKα1α2fl/fl mice, but not in AMPKα1α2fl/fl+AlbCre mice. Training increased liver triacylglycerides and the desaturation and elongation of fatty acids in triacylglycerides of AMPKα1α2fl/fl+AlbCre mice. These lipid responses were independent of differences in tricarboxylic acid cycle fluxes. In conclusion, AMPK is required for liver training adaptations that are critical to glucose and lipid metabolism.NEW & NOTEWORTHY This study shows that the energy sensor and transducer, AMP-activated protein kinase (AMPK), is necessary for an exercise training-induced: 1) increase in liver glycogen that is necessary for accelerated glycogenolysis during exercise, 2) decrease in liver glycerolipids independent of tricarboxylic acid (TCA) cycle flux, and 3) decline in the desaturation and elongation of fatty acids comprising liver diacylglycerides. The mechanisms defined in these studies have implications for use of regular exercise or AMPK-activators in patients with fatty liver.

Post-hepatectomy liver failure: A timeline centered review

BACKGROUND

Post-hepatectomy liver failure (PHLF) is a leading cause of postoperative mortality after liver surgery. Due to its significant impact, it is imperative to understand the risk stratification and preventative strategies for PHLF. The main objective of this review is to highlight the role of these strategies in a timeline centered way around curative resection.

DATA SOURCES

This review includes studies on both humans and animals, where they addressed PHLF. A literature search was conducted across the Cochrane Library, Embase, MEDLINE/PubMed, and Web of Knowledge electronic databases for English language studies published between July 1997 and June 2020. Studies presented in other languages were equally considered. The quality of included publications was assessed using Downs and Black's checklist. The results were presented in qualitative summaries owing to the lack of studies qualifying for quantitative analysis.

RESULTS

This systematic review with 245 studies, provides insight into the current prediction, prevention, diagnosis, and management options for PHLF. This review highlighted that liver volume manipulation is the most frequently studied preventive measure against PHLF in clinical practice, with modest improvement in the treatment strategies over the past decade.

CONCLUSIONS

Remnant liver volume manipulation is the most consistent preventive measure against PHLF.

Exercise training induces depot-specific remodeling of protein secretion in skeletal muscle and adipose tissue of obese male mice

Acute exercise induces changes in circulating proteins, which are known to alter metabolism and systemic energy balance. Skeletal muscle is a primary contributor to changes in the plasma proteome with acute exercise. An important consideration when assessing the endocrine function of muscle is the presence of different fiber types, which show distinct functional and metabolic properties and likely secrete different proteins. Similarly, adipokines are important regulators of systemic metabolism and have been shown to differ between depots. Given the health-promoting effects of exercise, we proposed that understanding depot-specific remodeling of protein secretion in muscle and adipose tissue would provide new insights into intertissue communication and uncover novel regulators of energy homeostasis. Here, we examined the effect of endurance exercise training on protein secretion from fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus muscle and visceral and subcutaneous adipose tissue. High-fat diet-fed mice were exercise trained for 6 wk, whereas a Control group remained sedentary. Secreted proteins from excised EDL and soleus muscle, inguinal, and epididymal adipose tissues were detected using mass spectrometry. We detected 575 and 784 secreted proteins from EDL and soleus muscle and 738 and 920 proteins from inguinal and epididymal adipose tissue, respectively. Of these, 331 proteins were secreted from all tissues, whereas secretion of many other proteins was tissue and depot specific. Exercise training led to substantial remodeling of protein secretion from EDL, whereas soleus showed only minor changes. Myokines released exclusively from EDL or soleus were associated with glycogen metabolism and cellular stress response, respectively. Adipokine secretion was completely refractory to exercise regulation in both adipose depots. This study provides an in-depth resource of protein secretion from muscle and adipose tissue, and its regulation following exercise training, and identifies distinct depot-specific secretion patterns that are related to the metabolic properties of the tissue of origin.NEW & NOTEWORTHY The present study examines the effects of exercise training on protein secretion from fast-twitch and slow-twitch muscle as well as visceral and subcutaneous adipose tissue of obese mice. Although exercise training leads to substantial remodeling of protein secretion from fast-twitch muscle, adipose tissue is completely refractory to exercise regulation.

Microbiota Mediate Enhanced Exercise Capacity Induced by Exercise Training

PURPOSE

We investigated the effects of gut microbes, and the mechanisms mediating the enhanced exercise performance induced by exercise training, i.e., skeletal muscle blood flow, and mitochondrial biogenesis and oxidative function in male mice.

METHODS

All mice received a graded exercise test before (PRE) and after exercise training via forced treadmill running at 60% to 70% of maximal running capacity 5 d·wk -1 for 5 wk (POST). To examine the role of the gut microbes, the graded exercise was repeated after 7 d of access to antibiotic (ABX)-treated water, used to eliminate gut microbes. Peripheral blood flow, mitochondrial oxidative capacity, and markers of mitochondrial biogenesis were collected at each time point.

RESULTS

Exercise training led to increases of 60% ± 13% in maximal running distance and 63% ± 11% work to exhaustion ( P < 0.001). These increases were abolished after ABX ( P < 0.001). Exercise training increased hindlimb blood flow and markers of mitochondrial biogenesis and oxidative function, including AMP-activated protein kinase, sirtuin-1, PGC-1α citrate synthase, complex IV, and nitric oxide, all of which were also abolished by ABX treatment.

CONCLUSIONS

Our results support the concept that gut microbiota mediate enhanced exercise capacity after exercise training and the mechanisms responsible, i.e., hindlimb blood flow, mitochondrial biogenesis, and metabolic profile. Finally, results of this study emphasize the need to fully examine the impact of prescribing ABX to athletes during their training regimens and how this may affect their performance.

Roles of malate and aspartate in gluconeogenesis in various physiological and pathological states

Gluconeogenesis, a pathway for glucose synthesis from non-carbohydrate substances, begins with the synthesis of oxaloacetate (OA) from pyruvate and intermediates of citric acid cycle in hepatocyte mitochondria. The traditional view is that OA does not cross the mitochondrial membrane and must be shuttled to the cytosol, where most enzymes involved in gluconeogenesis are compartmentalized, in the form of malate. Thus, the possibility of transporting OA in the form of aspartate has been ignored. In the article is shown that malate supply to the cytosol increases only when fatty acid oxidation in the liver is activated, such as during starvation or untreated diabetes. Alternatively, aspartate synthesized from OA by mitochondrial aspartate aminotransferase (AST) is transported to the cytosol in exchange for glutamate via the aspartate-glutamate carrier 2 (AGC2). If the main substrate for gluconeogenesis is an amino acid, aspartate is converted to OA via urea cycle, therefore, ammonia detoxification and gluconeogenesis are simultaneously activated. If the main substrate is lactate, OA is synthesized by cytosolic AST, glutamate is transported to the mitochondria through AGC2, and nitrogen is not lost. It is concluded that, compared to malate, aspartate is a more suitable form of OA transport from the mitochondria for gluconeogenesis.

The Efficient Synthesis and Anti-Fatigue Activity Evaluation of Macamides: The Unique Bioactive Compounds in Maca

Macamides are a class of amide alkaloids that are only found in maca and are widely considered to be its bioactive marker compounds. More than thirty macamide monomers have been identified in recent years; however, it is difficult to obtain a single macamide monomer from the maca plant because of their similar structures and characteristics. We used the carbodiimide condensation method (CCM) to efficiently synthesize five typical macamides, including N-benzyl-hexadecanamide (NBH), N-benzyl-9Z,12Z,15Z-octadecenamide, N-(3-methoxybenzyl)-9Z,12Z-octadecenamide, N-benzyl-9Z,12Z-octadecenamide, and N-(3-methoxybenzyl)-9Z,12Z,15Z-octadecadienamide. All the synthesized macamides were purified by a one-step HPLC with a purity of more than 95%. NBH is the most abundant macamide monomer in natural maca, and it was selected to evaluate the anti-fatigue effects of macamides. The results indicated that NBH could enhance the endurance capacity of mice by increasing liver glycogen levels and decreasing blood urea nitrogen, lactate dehydrogenase, blood ammonia, and blood lactic acid levels. Macamides might be the active substances that give maca its anti-fatigue active function.

Exercise and inactivity as modifiers of β cell function and type 2 diabetes risk

Exercise and regular physical activity are beneficial for the prevention and management of metabolic diseases such as obesity and type 2 diabetes, whereas exercise cessation, defined as deconditioning from regular exercise or physical activity that has lasted for a period of months to years, can lead to metabolic derangements that drive disease. Adaptations to the insulin-secreting pancreatic β-cells are an important benefit of exercise, whereas less is known about how exercise cessation affects these cells. Our aim is to review the impact that exercise and exercise cessation have on β-cell function, with a focus on the evidence from studies examining glucose-stimulated insulin secretion (GSIS) using gold-standard techniques. Potential mechanisms by which the β-cell adapts to exercise, including exerkine and incretin signaling, autonomic nervous system signaling, and changes in insulin clearance, will also be explored. We will highlight areas for future research.

Sexually dimorphic hepatic mitochondrial adaptations to exercise: a mini-review

Exercise is a physiological stress that disrupts tissue and cellular homeostasis while enhancing systemic metabolic energy demand mainly through the increased workload of skeletal muscle. Although the extensive focus has been on skeletal muscle adaptations to exercise, the liver senses these disruptions in metabolic energy homeostasis and responds to provide the required substrates to sustain increased demand. Hepatic metabolic flexibility is an energetically costly process that requires continuous mitochondrial production of the cellular currency ATP. To do so, the liver must maintain a healthy functioning mitochondrial pool, attained through well-regulated and dynamic processes. Intriguingly, some of these responses are sex-dependent. This mini-review examines the hepatic mitochondrial adaptations to exercise with a focus on sexual dimorphism.

Exercise training restores weight gain and attenuates hepatic inflammation in a rat model of non-celiac gluten sensitivity

Gluten intolerance is associated with several disorders in the body. Although research has grown in recent years, the understanding of its impact on different tissues and the effects of physical exercise in mitigating health problems in the condition of gluten intolerance are still limited. Therefore, our objective was to test whether gliadin would affect metabolism and inflammation in liver tissue and whether aerobic physical exercise would mitigate the negative impacts of gliadin administration in rodents. Wistar rats were divided into exercised gliadin, gliadin, and control groups. Gliadin was administered by gavage from birth to 60 days of age. The rats in the exercised gliadin group performed an aerobic running exercise training protocol for 15 days. At the end of the experiments, physiological, histological, and molecular analyzes were performed in the study. Compared to the control group, the gliadin group had impaired weight gain and increased gluconeogenesis, lipogenesis, and inflammatory biomarkers in the liver. On the other hand, compared to the gliadin group, animals in the exercise-gliadin group had a recovery in body weight, improved insulin sensitivity, and a reduction in some gluconeogenesis, lipogenesis, and inflammatory biomarkers in the liver. In conclusion, our results revealed that the administration of gliadin from birth impaired weight gain and induced an increase in hepatic inflammatory cytokines, which was associated with an impairment of glycemic homeostasis in the liver, all of which were attenuated by adding aerobic exercise training in the gliadin group.

The role of exercise and hypoxia on glucose transport and regulation

Muscle glucose transport activity increases with an acute bout of exercise, a process that is accomplished by the translocation of glucose transporters to the plasma membrane. This process remains intact in the skeletal muscle of individuals with insulin resistance and type 2 diabetes mellitus (T2DM). Exercise training is, therefore, an important cornerstone in the management of individuals with T2DM. However, the acute systemic glucose responses to carbohydrate ingestion are often augmented during the early recovery period from exercise, despite increased glucose uptake into skeletal muscle. Accordingly, the first aim of this review is to summarize the knowledge associated with insulin action and glucose uptake in skeletal muscle and apply these to explain the disparate responses between systemic and localized glucose responses post-exercise. Herein, the importance of muscle glycogen depletion and the key glucoregulatory hormones will be discussed. Glucose uptake can also be stimulated independently by hypoxia; therefore, hypoxic training presents as an emerging method for enhancing the effects of exercise on glucose regulation. Thus, the second aim of this review is to discuss the potential for systemic hypoxia to enhance the effects of exercise on glucose regulation.

Cutting edge concepts: Does bilirubin enhance exercise performance?

Exercise performance is dependent on many factors, such as muscular strength and endurance, cardiovascular capacity, liver health, and metabolic flexibility. Recent studies show that plasma levels of bilirubin, which has classically been viewed as a liver dysfunction biomarker, are elevated by exercise training and that elite athletes may have significantly higher levels. Other studies have shown higher plasma bilirubin levels in athletes and active individuals compared to general, sedentary populations. The reason for these adaptions is unclear, but it could be related to bilirubin's antioxidant properties in response to a large number of reactive oxygen species (ROS) that originates from mitochondria during exercise. However, the mechanisms of these are unknown. Current research has re-defined bilirubin as a metabolic hormone that interacts with nuclear receptors to drive gene transcription, which reduces body weight. Bilirubin has been shown to reduce adiposity and improve the cardiovascular system, which might be related to the adaption of bilirubin increasing during exercise. No studies have directly tested if elevating bilirubin levels can influence athletic performance. However, based on the mechanisms proposed in the present review, this seems plausible and an area to consider for future studies. Here, we discuss the importance of bilirubin and exercise and how the combination might improve metabolic health outcomes and possibly athletic performance.

Can melatonin reduce the severity of post-COVID-19 syndrome?

This short review aimed at (i) providing an update on the health benefits associated with melatonin supplementation, while (ii) considering future potential research directions concerning melatonin supplementation use relative to Coronavirus disease of 2019 (COVID-19). A narrative review of the literature was undertaken to ascertain the effect of exogenous melatonin administration on humans. Night-time melatonin administration has a positive impact on human physiology and mental health. Indeed, melatonin (i) modulates the circadian components of the sleep-wake cycle; (ii) improves sleep efficiency and mood status; (iii) improves insulin sensitivity; and (iv) reduces inflammatory markers and oxidative stress. Melatonin has also remarkable neuroprotective and cardioprotective effects and may therefore prevent deterioration caused by COVID-19. We suggest that melatonin could be used as a potential therapy in the post-COVID-19 syndrome, and therefore call for action the research community to investigate on the potential use of exogenous melatonin to enhance the quality of life in patients with post-COVID-19 syndrome. See also Figure 1(Fig. 1).

Loss of hepatic phosphoenolpyruvate carboxykinase 1 dysregulates metabolic responses to acute exercise but enhances adaptations to exercise training in mice

Acute exercise increases liver gluconeogenesis to supply glucose to working muscles. Concurrently, elevated liver lipid breakdown fuels the high energetic cost of gluconeogenesis. This functional coupling between liver gluconeogenesis and lipid oxidation has been proposed to underlie the ability of regular exercise to enhance liver mitochondrial oxidative metabolism and decrease liver steatosis in individuals with nonalcoholic fatty liver disease. Herein we tested whether repeated bouts of increased hepatic gluconeogenesis are necessary for exercise training to lower liver lipids. Experiments used diet-induced obese mice lacking hepatic phosphoenolpyruvate carboxykinase 1 (KO) to inhibit gluconeogenesis and wild-type (WT) littermates. 2H/13C metabolic flux analysis quantified glucose and mitochondrial oxidative fluxes in untrained mice at rest and during acute exercise. Circulating and tissue metabolite levels were determined during sedentary conditions, acute exercise, and refeeding postexercise. Mice also underwent 6 wk of treadmill running protocols to define hepatic and extrahepatic adaptations to exercise training. Untrained KO mice were unable to maintain euglycemia during acute exercise resulting from an inability to increase gluconeogenesis. Liver triacylglycerides were elevated after acute exercise and circulating β-hydroxybutyrate was higher during postexercise refeeding in untrained KO mice. In contrast, exercise training prevented liver triacylglyceride accumulation in KO mice. This was accompanied by pronounced increases in indices of skeletal muscle mitochondrial oxidative metabolism in KO mice. Together, these results show that hepatic gluconeogenesis is dispensable for exercise training to reduce liver lipids. This may be due to responses in ketone body metabolism and/or metabolic adaptations in skeletal muscle to exercise.NEW & NOTEWORTHY Exercise training reduces hepatic steatosis partly through enhanced hepatic terminal oxidation. During acute exercise, hepatic gluconeogenesis is elevated to match the heightened rate of muscle glucose uptake and maintain glucose homeostasis. It has been postulated that the hepatic energetic stress induced by elevating gluconeogenesis during acute exercise is a key stimulus underlying the beneficial metabolic responses to exercise training. This study shows that hepatic gluconeogenesis is not necessary for exercise training to lower liver lipids.

Continuous glucose monitoring assessment in patients suffering from anorexia nervosa reveals chronic prolonged mild hypoglycemia all over the nycthemeron

OBJECTIVE

Anorexia nervosa (AN) is an eating disorder characterised by voluntary dietary restriction leading to severe undernutrition. Hypoglycaemia is mostly described through severe case reports and is always evaluated by fasting or post-meal blood glucose, showing nothing about hypoglycaemia's length or duration. The interest of continuous interstitial glucose monitoring (CGM), largely used in diabetes mellitus, has never been evaluated in AN patients.

METHOD

Glycaemia cycles in AN patients were assessed using CGM over 5 days and then analysed according to food intake.

RESULTS

Mean glycaemia was within normal range. 91% of the patients presented with at least one episode with glycaemia under 70 mg/dl. Within the 24 h, the percentage of time spent with a glycaemia under 70 mg/dl was of 20.82 ± 3.90% with a maximum of 52%. We found 2.52 ± 0.33 hypoglycaemia events per 24 h, including 21.11 ± 3.76% at night. CGM parameters correlated with cortisol and IGF1 plasma levels. Comparison with estimated carbohydrate intakes discriminated concordant and non-concordant estimations depending on patient.

CONCLUSIONS

AN patients display chronic prolonged mild hypoglycaemia all over the nycthemeron despite normal fasting glycaemia. Associated adaptive increased counter-regulatory hormones might protect AN patients from deeper hypoglycaemia. CGM allowed testing food intake self-estimation reliability of AN patients and could be a very useful biofeedback tool.

Long-Term Aerobic Training Improves Mitochondrial and Antioxidant Function in the Liver of Wistar Rats Preventing Hepatic Age-Related Function Decline

Most studies on the effects of physical exercise have focused on its influence on muscle tissue, forgetting its interference in liver function. Ageing leads to the progressive impairment of hepatic functions. Several biochemical and bioenergetics parameters were determined to test the impact of a lifelong aerobic training program in the hepatic age-related and the development of an adaptative response. Liver samples were collected from 28 male Wistar rats (4-week-old, 159.4 ± 11.9 g at the beginning of the protocol), randomly distributed into two groups: non-exercised or exercised and submitted to a treadmill exercise program (60 min/day, 5 days/week, at 70% of maximal running speed), for 24 (n = 9) or 54 weeks (n = 10). A maximal running speed test was performed to determine the training speed. Antioxidant enzyme activity, cellular redox status, oxidative stress, mitochondrial respiratory chain enzymes and respiratory activity were performed in liver samples. Lifelong exercise decreased the age-associated decline in mitochondrial dysfunction, increasing the respiratory rate in state 2 (mitochondrial respiration stimulated by the substrate in the absence of added ADP) (p = 0.03) and citrate synthase enzymatic activity (p = 0.007). Complex II (p < 0.0001) and IV (p < 0.001) showed a decrease in enzymatic activity. Ageing-related oxidative stress was also attenuated by physical exercise, as showed by the increase in first-line defense antioxidant enzymes (superoxide dismutase (p = 0.07) and catalase (p = 0.03)), decreased lipid peroxidation levels (p = 0.864 for total fraction, p = 0,27 for mitochondrial fraction) and higher glutathione reduced/oxidized ratio (p = 0.02). According to our results, the regular practice of exercise can prevent the liver’s mitochondrial dysfunction and loss of antioxidant system efficacy that may arise from ageing, highlighting the benefit of lifelong aerobic exercise in preventing age-related hepatic impairment and associated diseases.

Chrono-exercise: Time-of-day-dependent physiological responses to exercise

Exercise is an effective strategy to prevent and improve obesity and related metabolic diseases. Exercise increases the metabolic demand in the body. Although many of the metabolic health benefits of exercise depend on skeletal muscle adaptations, exercise exerts many of its metabolic effects through the liver, adipose tissue, and pancreas. Therefore, exercise is the physiological state in which inter-organ signaling is most important. By contrast, circadian rhythms in mammals are associated with the regulation of several physiological and biological functions, including body temperature, sleep-wake cycle, physical activity, hormone secretion, and metabolism, which are controlled by clock genes. Glucose and lipid tolerance reportedly exhibit diurnal variations, being lower in the evening than in the morning. Therefore, the effects of exercise on substrate metabolism at different times of the day may differ. In this review, the importance of exercise timing considerations will be outlined, incorporating a chrono-exercise perspective.

Acute exercise dynamically modulates the hepatic mitochondrial proteome

Exercise powerfully increases energy metabolism and substrate flux in tissues, a process reliant on dramatic changes in mitochondrial energetics. Liver mitochondria play a multi-factorial role during exercise to fuel hepatic glucose output. We previously showed acute exercise activates hepatic mitophagy, a pathway to recycle low-functioning/damaged mitochondria, however little is known how individual bouts of exercise alters the hepatic mitochondrial proteome. Here we leveraged proteomics to examine changes in isolated hepatic mitochondria both immediately after and 2 hours post an acute, 1 hour bout of treadmill exercise in female mice. Further, we utilized leupeptin, a lysosomal inhibitor, to capture and measure exercise-induced changes in mitochondrial proteins that would have been unmeasured due to their targeting for lysosomal degradation. Proteomic analysis of enriched hepatic mitochondria identified 3241 total proteins. Functional enrichment analysis revealed robust enrichment for proteins critical to the mitochondria including metabolic pathways, tricarboxylic acid cycle, and electron transport system. Compared to the sedentary condition, exercise elevated processes regulating lipid localization, Il-5 signaling, and protein phosphorylation in isolated mitochondria. t-SNE analysis identified 4 unique expressional clusters driven by time-dependent changes in protein expression. Isolation of proteins significantly altered with exercise from each cluster revealed influences of leupeptin and exercise both independently and cooperatively modulating mitochondrial protein expressional profiles. Overall, we provide evidence that acute exercise rapidly modulates changes in the proteins/pathways of isolated hepatic mitochondria that include fatty acid metabolism/storage, post-translational protein modification, inflammation, and oxidative stress. In conclusion, the hepatic mitochondrial proteome undergoes extensive remodeling with a bout of exercise.

Addition of Fructose to a Carbohydrate-Rich Breakfast Improves Cycling Endurance Capacity in Trained Cyclists

It was previously demonstrated that postexercise ingestion of fructose-glucose mixtures can lead to superior liver and equal muscle glycogen synthesis as compared with glucose-based carbohydrates (CHOs) only. After an overnight fast, liver glycogen stores are reduced, and based on this we hypothesized that addition of fructose to a glucose-based breakfast would lead to improved subsequent endurance exercise capacity. In this double-blind cross-over randomized study (eight males, peak oxygen uptake: 62.2 ± 5.4 ml·kg-1·min-1), participants completed two experimental trials consisting of two exercise bouts. In the afternoon of Day 1, they completed a cycling interval training session to normalize glycogen stores after which a standardized high-CHO diet was provided for 4 hr. On Day 2, in the morning, participants received 2 g/kg of CHOs in the form of glucose and rice or fructose and rice, both in a CHO ratio of 1:2. Two hours later they commenced cycling exercise session at the intensity of the first ventilatory threshold until task failure. Exercise capacity was higher in fructose and rice (137.0 ± 22.7 min) as compared with glucose and rice (130.06 ± 19.87 min; p = .046). Blood glucose and blood lactate did not differ between the trials (p > .05) and neither did CHO and fat oxidation rates (p > .05). However, due to the duration of exercise, total CHO oxidation was higher in fructose and rice (326 ± 60 g vs. 298 ± 61 g, p = .009). Present data demonstrate that addition of fructose to a glucose-based CHO source at breakfast improves endurance exercise capacity. Further studies are required to determine the mechanisms and optimal dose and ratio.

Cellular and Molecular Regulation of Exercise—A Neuronal Perspective

The beneficial effects of exercise on the proper functioning of the body have been firmly established. Multi-systemic metabolic regulation of exercise is the consequence of multitudinous changes that occur at the cellular level. The exercise responsome comprises all molecular entities including exerkines, miRNA species, growth factors, signaling proteins that are elevated and activated by physical exercise. Exerkines are secretory molecules released by organs such as skeletal muscle, adipose tissue, liver, and gut as a function of acute/chronic exercise. Exerkines such as FNDC5/irisin, Cathepsin B, Adiponectin, and IL-6 circulate through the bloodstream, cross the blood-brain barrier, and modulate the expression of important signaling molecules such as AMPK, SIRT1, PGC1α, BDNF, IGF-1, and VEGF which further contribute to improved energy metabolism, glucose homeostasis, insulin sensitivity, neurogenesis, synaptic plasticity, and overall well-being of the body and brain. These molecules are also responsible for neuroprotective adaptations that exercise confers on the brain and potentially ameliorate neurodegeneration. This review aims to detail important cellular and molecular species that directly or indirectly mediate exercise-induced benefits in the body, with an emphasis on the central nervous system.

Proteomic analysis of the effect of high-fat-diet and voluntary physical activity on mouse liver

Nonalcoholic fatty liver disease (NALFD), characterized by an abnormal accumulation of triglycerides in hepatocytes, is closely linked to insulin resistance, metabolic syndrome, and changes in lipogenesis in the liver. The accumulation of hepatic lipids can lead to a range of pathologies from mild steatosis to severe cirrhosis. Endurance exercise is known to ameliorate the adverse health effects of NAFLD. Therefore, we aimed to investigate the effect of voluntary wheel running (VWR) on the metabolic changes in the livers of high-fat diet (HFD)-induced NAFLD mice and used LC-MS/MS (Liquid chromatography–mass spectrometry) to determine whether the tested intervention affected the protein expression profiles of the mouse livers. Male C57BL/6 mice were randomly divided into three groups: control (CON), high-fat diet sedentary group (HFD), high-fat diet VWR group (HFX). HFX group performed voluntary wheel running into individually cages, given a high-fat diet for 12 weeks. Food consumption, body weight, and running distance were measured every week. Using 2D (2-dimensional)-gel electrophoresis, we detected and quantitatively analyzed the protein expression with >2.0-fold change in the livers of HFD-fed mice, HFD-fed exercise (HFX) mice, and chow-fed mice. Body weight was significantly increased in HFD compared to CON (P < 0.05). The 2D-gel electrophoresis analysis indicated that there was a difference between CON and HFD groups, showing 31 increased and 27 decreased spots in the total 302 paired spots in the HFD group compared to CON. The analysis showed 43 increased and 17 decreased spots in the total 258 spots in the HFX group compared to CON. Moreover, 12 weeks of VWR showed an increase of 35 and a decrease of 8 spots in a total of 264 paired spots between HFD and HFX. LC-MS/MS of HFD group revealed that proteins involved in ketogenesis, lipid metabolism, and the metabolism of drugs and xenobiotics were upregulated, whereas detoxifying proteins, mitochondrial precursors, transport proteins, proteasomes, and proteins involved in amino acid metabolism were downregulated. On the other hand, VWR counteracted the protein expression profile of HFD-fed mice by upregulating molecular chaperones, gluconeogenesis-, detoxification-, proteasome-, and energy metabolism-related proteins. This study provided a molecular understanding of the HFD- and exercise-induced protein marker expression and presented the beneficial effects of exercise during pathophysiological conditions.

Hypothesis: Enhanced glucose availability and insulin resistance enhances an activated immune system and accounts for the obesity paradox

Many studies have demonstrated an 'obesity paradox' where people with obesity have reduced mortality in the context of acute critical illnesses compared to people of normal weight. In contrast, obesity is associated with reduced life expectancy in the population in general and is associated with an increased risk for type 2 diabetes, cardiovascular disease and other health problems. However, the absence of the metabolic syndrome is associated a lower mortality than when the metabolic syndrome is present regardless of body mass index status and the obesity paradox appears to only occur in association with the metabolic syndrome, but cardiorespiratory fitness modifies these outcomes. Enhanced glucose availability is important when the immune system is activated not only because it has an acute onset, a high consumption of glucose and is substantially an obligate glucose utilizer but also because it has priority over most other tissues and cells for the available glucose. Thus, for vulnerable populations, such as children with severe infections, this increases the risk of hypoglycaemia and death. The obesity paradox may be substantially a consequence of two features associated with obesity. One is endogenous glucose production (EGP). Obesity is associated with an increased capacity for EGP and thus is associated with enhanced glucose availability. Second is insulin resistance that reduces the amount of glucose metabolized by cells that are not obligate glucose utilizers and increases the release of fatty acids and glycerol from adipose stores that are alternative fuels for tissues and cells.

The pathophysiology of motor fatigue and fatigability in multiple sclerosis

Multiple Sclerosis (MS) is a heterogeneous immune mediated disease of the central nervous system (CNS). Fatigue is one of the most common and disabling symptom of MS. It interferes with daily activities on the level of cognition and motor endurance. Motor fatigue can either result from lesions in cortical networks or motor pathways (“primary fatigue”) or it may be a consequence of detraining with subsequent adaptions of muscle and autonomic function. Programmed exercise interventions are used frequently to increase physical fitness in MS-patients. Studies investigating the effects of training on aerobic capacity, objective endurance and perceived fatigability have yielded heterogenous results, most likely due to the heterogeneity of interventions and patients, but probably also due to the non-uniform pathophysiology of fatigability among MS-patients. The aim of this review is to summarize the current knowledge on the pathophysiology of motor fatigability with special reference to the basic exercise physiology that underlies our understanding of both pathogenesis and treatment interventions.

Circulating cell-free DNA in health and disease - the relationship to health behaviours, ageing phenotypes and metabolomics

Circulating cell-free DNA (cf-DNA) has emerged as a promising biomarker of ageing, tissue damage and cellular stress. However, less is known about health behaviours, ageing phenotypes and metabolic processes that lead to elevated cf-DNA levels. We sought to analyse the relationship of circulating cf-DNA level to age, sex, smoking, physical activity, vegetable consumption, ageing phenotypes (physical functioning, the number of diseases, frailty) and an extensive panel of biomarkers including blood and urine metabolites and inflammatory markers in three human cohorts (N = 5385; 17-82 years). The relationships were assessed using correlation statistics, and linear and penalised regressions (the Lasso), also stratified by sex.cf-DNA levels were significantly higher in men than in women, and especially in middle-aged men and women who smoke, and in older more frail individuals. Correlation statistics of biomarker data showed that cf-DNA level was higher with elevated inflammation (C-reactive protein, interleukin-6), and higher levels of homocysteine, and proportion of red blood cells and lower levels of ascorbic acid. Inflammation (C-reactive protein, glycoprotein acetylation), amino acids (isoleucine, leucine, tyrosine), and ketogenesis (3-hydroxybutyrate) were included in the cf-DNA level-related biomarker profiles in at least two of the cohorts.In conclusion, circulating cf-DNA level is different by sex, and related to health behaviour, health decline and metabolic processes common in health and disease. These results can inform future studies where epidemiological and biological pathways of cf-DNA are to be analysed in details, and for studies evaluating cf-DNA as a potential clinical marker.

Nitrate exposure reprograms hepatic amino acid and nutrient sensing pathways prior to exercise: A metabolomic and transcriptomic investigation in zebrafish (Danio rerio)

Scope: Nitrate supplementation is a popular ergogenic aid that improves exercise performance by reducing oxygen consumption during exercise. We investigated the effect of nitrate exposure and exercise on metabolic pathways in zebrafish liver.

Materials and methods: Fish were exposed to sodium nitrate (606.9 mg/L), or control water, for 21 days and analyzed at intervals during an exercise test. We utilized untargeted liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis and measured gene expression of 24 genes central to energy metabolism and redox signaling.

Results: We observed a greater abundance of metabolites involved in endogenous nitric oxide (NO) metabolism and amino acid metabolism in nitrate-treated liver at rest, compared to rested controls. In the absence of exercise, nitrate treatment upregulated expression of genes central to nutrient sensing (pgc1a), protein synthesis (mtor) and purine metabolism (pnp5a and ampd1) and downregulated expression of genes involved in mitochondrial fat oxidation (acaca and cpt2).

Conclusion: Our data support a role for sub-chronic nitrate treatment in the improvement of exercise performance, in part, by improving NO bioavailability, sparing arginine, and modulating hepatic gluconeogenesis and glycolytic capacity in the liver.

Low-Volume Sprint Interval Swimming Is Sufficient to Increase Blood Metabolic Biomarkers in Master Swimmers

Purpose: Sprint interval exercise is a time-efficient way of inducing beneficial adaptations. However, little is known about its minimal effective volume, especially in swimming. The aim of the present study was to evaluate and compare the effects of two sprint interval swimming sets of different low volumes on blood biomarkers. Method: Twenty-one master swimmers [11 females aged 38.5 (8.5) years, 10 males aged 42.7 (5.7) years] completed two freestyle swimming sets of 4 × 50 m and 4 × 25 m at maximal intensity and a work-to-rest ratio of 1:1, on different days, in random and counterbalanced order. Blood samples were taken before, immediately after and one hour after exercise for determination of a number of biochemical parameters. Results: Swimming speed was higher in the 4 × 25-m set. Lactate, glucose, insulin, glucagon, cortisol, and reduced glutathione increased immediately post-exercise, while uric acid increased 1 h post-exercise (p < .05). All aforementioned biomarkers, excluding glucagon, increased more with the 4 × 50-m set, compared to the 4 × 25-m set (p < .05). Session rating of perceived exertion was higher after the 4 × 50-m set (p = .011). Conclusion: Both sprint interval swimming sets elicited increases in blood biomarkers in master swimmers. The set of higher volume elicited greater increases in most of the biochemical markers studied but also in subjective load. Thus, although the set of higher volume was more efficient in perturbing blood biomarkers, even the very low-volume set induced metabolic stress that may trigger adaptive mechanisms.

Lactate modulates cardiac gene expression in mice during acute physical exercise

The aim of the present study was to verify the role of lactate as a signaling molecule in cardiac tissue under physiological conditions. C57BL6/J male mice were submitted to acute running bouts on a treadmill at different exercise intensities (30, 60, and 90% of maximal speed - Smax) under the effect of two doses (0.5 and 5 mM) of α-cyano-4-hydroxycynnamate (CINN), a blocker of lactate transporters. Cardiac lactate levels, activity of the enzymes of glycolytic [hexokinase (HK) and lactate dehydrogenase (LDH)] and oxidative metabolism [citrate synthase (CS)], and expression of genes also related to metabolism [LDH, nuclear factor erythroid 2-related factor 2 (NRF-2), cytochrome oxidase IV (COX-IV), and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α)] were evaluated. Elevated cardiac lactate levels were observed after high intensity running at 90% of Smax, which were parallel to increased activity of the HK and CS enzymes and mRNA levels of PGC-1α and COX-IV. No changes were observed in cardiac lactate levels in mice running at lower exercise intensities. Interestingly, prior intraperitoneal administration (15 min) of CINN (0.5 mM) significantly reduced cardiac lactate concentration, activities of HK and CS, and mRNA levels of PGC-1α and COX-IV in mice that ran at 90% of Smax. In addition, cardiac lactate levels were significantly correlated to both PGC-1α and COX-IV cardiac gene expression. The present study provides evidence that cardiac lactate levels are associated to gene transcription during an acute bout of high intensity running exercise.

Proteomic analysis reveals exercise training induced remodelling of hepatokine secretion and uncovers syndecan-4 as a regulator of hepatic lipid metabolism

Objective

Non-alcoholic fatty liver disease (NAFLD) is linked to impaired lipid metabolism and systemic insulin resistance, which is partly mediated by altered secretion of liver proteins known as hepatokines. Regular physical activity can resolve NAFLD and improve its metabolic comorbidities, however, the effects of exercise training on hepatokine secretion and the metabolic impact of exercise-regulated hepatokines in NAFLD remain unresolved. Herein, we examined the effect of endurance exercise training on hepatocyte secreted proteins with the aim of identifying proteins that regulate metabolism and reduce NAFLD severity.

Methods

C57BL/6 mice were fed a high-fat diet for six weeks to induce NAFLD. Mice were exercise trained for a further six weeks, while the control group remained sedentary. Hepatocytes were isolated two days after the last exercise bout, and intracellular and secreted proteins were detected using label-free mass spectrometry. Hepatocyte secreted factors were applied to skeletal muscle and liver ex vivo and insulin action and fatty acid metabolism were assessed. Syndecan-4 (SDC4), identified as an exercise-responsive hepatokine, was overexpressed in the livers of mice using adeno-associated virus. Whole-body energy homeostasis was assessed by indirect calorimetry and skeletal muscle and liver metabolism was assessed using radiometric techniques.

Results

Proteomics analysis detected 2657 intracellular and 1593 secreted proteins from mouse hepatocytes. Exercise training remodelled the hepatocyte proteome, with differences in 137 intracellular and 35 secreted proteins. Bioinformatic analysis of hepatocyte secreted proteins revealed enrichment of tumour suppressive proteins and proteins involved in lipid metabolism and mitochondrial function, and suppression of oncogenes and regulators of oxidative stress. Hepatocyte secreted factors from exercise trained mice improved insulin action in skeletal muscle and increased hepatic fatty acid oxidation. Hepatocyte-specific overexpression of SDC4 reduced hepatic steatosis, which was associated with reduced hepatic fatty acid uptake, and blunted pro-inflammatory and pro-fibrotic gene expression. Treating hepatocytes with recombinant ectodomain of SDC4 (secreted form) recapitulated these effects with reduced fatty acid uptake, lipid storage and lipid droplet accumulation.

Conclusions

Remodelling of hepatokine secretion is an adaptation to regular exercise training that induces changes in metabolism in the liver and skeletal muscle. SDC4 is a novel exercise-responsive hepatokine that decreases fatty acid uptake and reduces steatosis in the liver. By understanding the proteomic changes in hepatocytes with exercise, these findings have potential for the discovery of new therapeutic targets for NAFLD.

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Exercise training remodels hepatokine secretion.

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Exercise regulated secreted factors improve insulin action in skeletal muscle.

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Syndecan-4 (SDC4) is a novel exercise-induced hepatokine.

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SDC4 reduces hepatic fatty acid uptake and hepatic steatosis.

High-intensity interval resistance training (HIIRT) improves liver gluconeogenesis from lactate in Swiss mice

High-intensity physical exercise favors anaerobic glycolysis and increases lactatemia. Lactate is converted back to glucose in the liver, so that the lactate threshold, an indicator of physical performance, must be related to the gluconeogenic capacity of the liver. This research assessed the effect of a high-intensity interval resistance training (HIIRT) on liver gluconeogenesis from lactate. Swiss mice were trained (groups T) on vertical ladder with overload of 90% of their maximal load. Control animals remained untrained (groups C0 and C8). In situ liver perfusion with lactate and adrenaline was performed in rested mice after 6 hours of food deprivation. There were larger outputs of glucose (T6, 71.90%; T8, 54.53%) and pyruvate (T8, 129.28%) (representative values for 4 mM lactate) in the groups trained for 6 or 8 weeks (T6 and T8), and of glucose in the presence of adrenaline in group T8 (280%). The content of PEPCK, an important regulatory enzyme of the gluconeogenic pathway, was 69.13% higher in group T8 than in the age-matched untrained animals (C8). HIIRT augmented liver gluconeogenesis from lactate and this might improve the lactate threshold. Novelty: The liver metabolizes lactate from muscle into glucose. Physical training may enhance the gluconeogenic capacity of the liver. As lactate clearance by the liver improves, lactate threshold is displaced to higher exercise intensities.

State of Knowledge on Molecular Adaptations to Exercise in Humans: Historical Perspectives and Future Directions

For centuries, regular exercise has been acknowledged as a potent stimulus to promote, maintain, and restore healthy functioning of nearly every physiological system of the human body. With advancing understanding of the complexity of human physiology, continually evolving methodological possibilities, and an increasingly dire public health situation, the study of exercise as a preventative or therapeutic treatment has never been more interdisciplinary, or more impactful. During the early stages of the NIH Common Fund Molecular Transducers of Physical Activity Consortium (MoTrPAC) Initiative, the field is well-positioned to build substantially upon the existing understanding of the mechanisms underlying benefits associated with exercise. Thus, we present a comprehensive body of the knowledge detailing the current literature basis surrounding the molecular adaptations to exercise in humans to provide a view of the state of the field at this critical juncture, as well as a resource for scientists bringing external expertise to the field of exercise physiology. In reviewing current literature related to molecular and cellular processes underlying exercise-induced benefits and adaptations, we also draw attention to existing knowledge gaps warranting continued research effort. © 2021 American Physiological Society. Compr Physiol 12:3193-3279, 2022.

Acute exercise rapidly activates hepatic mitophagic flux

Exercise is critical for improving metabolic health and putatively maintains or enhances mitochondrial quality control in metabolic tissues. Although previous work has shown that exercise elicits hepatic mitochondrial biogenesis, it is unknown if acute exercise activates hepatic mitophagy, the selective degradation of damaged or low-functioning mitochondria. We tested if an acute bout of treadmill running increased hepatic mitophagic flux both right after and 2-h postexercise in 15- to 24-wk-old C57BL/6J female mice. Acute exercise did not significantly increase markers of autophagic flux, however, mitophagic flux was activated 2-h post-treadmill running as measured by accumulation of both LC3-II and p62 in isolated mitochondria in the presence of leupeptin, an inhibitor of autophagosome degradation. Furthermore, mitochondrial-associated ubiquitin, which recruits the autophagy receptor protein p62, was also significantly increased at 2 h. Further examination via Western blot and proteomics analysis revealed that acute exercise elicits a time-dependent, dynamic activation of mitophagy pathways. Moreover, the results suggest that exercise-induced hepatic mitophagy is likely mediated by both polyubiquitination and receptor-mediated signaling pathways. Overall, we provide evidence that acute exercise activates hepatic mitophagic flux while also revealing specific receptor-mediated proteins by which exercise maintains mitochondrial quality control in the liver.NEW & NOTEWORTHY This study provides evidence that acute exercise activates hepatic mitophagic flux and mitochondrial polyubiquitination while additionally revealing specific receptor-mediated proteins by which exercise maintains mitochondrial quality control in the liver.

Taurine supplementation enhances endurance capacity by delaying blood glucose decline during prolonged exercise in rats

Taurine enhances physical performance; however, the underlying mechanism remains unclear. This study examined the effect of taurine on the overtime dynamics of blood glucose concentration (BGC) during endurance exercise in rats. Male F344 rats were subjected to transient treadmill exercise until exhaustion following 3 weeks of taurine supplementation or non-supplementation (TAU and CON groups). Every 10 min during exercise, BGC was measured in blood collected through cannulation of the jugular vein. Gluconeogenesis-, lipolysis-, and fatty acid oxidation-related factors in the plasma, liver, and skeletal muscles were also analyzed after 120-min run. Exercise time to exhaustion was significantly longer with taurine supplementation. BGC in the two groups significantly increased by 40 min and gradually and significantly decreased toward the respective exhaustion point. The decline in BGC from the peak at 40 min was significantly slower in the TAU group. The time when the once-increased BGC regressed to the 0-time level was significantly and positively correlated with exercise time until exhaustion. At the 120-min point, where the difference in BGC between the two groups was most significant, plasma free fatty acid concentration and acetyl-carnitine and N-acetyltaurine concentrations in skeletal muscle were significantly higher in the TAU group, whereas glycogen and glucogenic amino acid concentrations and G6Pase activity in the liver were not different between the two groups. Taurine supplementation enhances endurance capacity by delaying the decrease in BGC toward exhaustion through increases of lipolysis in adipose tissues and fatty acid oxidation in skeletal muscles during endurance exercise.

Sex differences in endurance exercise capacity and skeletal muscle lipid metabolism in mice

Previous studies suggest that sex differences in lipid metabolism exist with females demonstrating a higher utilization of lipids during exercise, which is mediated partly by increased utilization of muscle triglycerides. However, whether these changes in lipid metabolism contribute directly to endurance exercise performance is unclear. Therefore, the objective of this study was to investigate the contribution of exercise substrate metabolism to sex differences in endurance exercise capacity (EEC) in mice. Male and female C57BL/6-NCrl mice were subjected to an EEC test until exhaustion on a motorized treadmill. The treadmill was set at a 10% incline, and the speed gradually increased from 10.2 m/min to 22.2 m/min at fixed intervals for up to 2.5 h. Tissues and blood were harvested in mice immediately following the EEC. A cohort of sedentary, non-exercised male and female mice were used as controls. Females outperformed males by ~25% on the EEC. Serum levels of both fatty acids and ketone bodies were ~50% higher in females at the end of the EEC. In sedentary female mice, skeletal muscle triglyceride content was significantly greater compared to sedentary males. Gene expression analysis demonstrated that genes involved in skeletal muscle fatty acid oxidation were significantly higher in females with no changes in genes associated with glucose uptake or ketone body oxidation. The findings suggest that female mice have a higher endurance exercise capacity and a greater ability to mobilize and utilize fatty acids for energy.

Factors mediating exercise-induced organ crosstalk

Exercise activates a plethora of metabolic and signalling pathways in skeletal muscle and other organs causing numerous systemic beneficial metabolic effects. Thus, regular exercise may ameliorate and prevent the development of several chronic metabolic diseases. Skeletal muscle is recognized as an important endocrine organ regulating systemic adaptations to exercise. Skeletal muscle may mediate crosstalk with other organs through the release of exercise-induced cytokines, peptides and proteins, termed myokines, into the circulation. Importantly, other tissues such as the liver and adipose tissue may also release cytokines and peptides in response to exercise. Hence, exercise-released molecules are collectively called exerkines. Moreover, extracellular vesicles (EVs), in the form of exosomes or microvesicles, may carry some of the signals involved in tissue crosstalk. This review focuses on the role of factors potentially mediating crosstalk between muscle and other tissues in response to exercise.

Mitigation of MAFLD in High Fat-High Sucrose-Fructose Fed Mice by a Combination of Genistein Consumption and Exercise Training

PURPOSE

Metabolic dysfunction-associated fatty liver disease (MAFLD) is fueled by escalations in both sedentary behavior and caloric intake and is noted in obese type 2 diabetic (T2DM) patients. This study aimed to examine the effects of exercise and the phytoestrogen genistein in mice fed a high fat (60% fat) high sugar (55% fructose with 45% sucrose), HFHS diet.

METHODS

Male C57BL/6J mice were assigned to five groups: HFHS, HFHS with genistein (600 mg/kg diet, HFHS+Gen), HFHS with moderate exercise (HFHS+Ex), and HFHS with combined genistein and moderate exercise (HFHS-Gen+Ex). Control lean mice were fed standard chow and water. Exercise consisted of 30-minute sessions of treadmill running five days/week for the 12-week study duration. Body weight was assessed weekly. Liver, kidney, fecal pellets and serum were extracted at the end of the study and maintained at -80°C.

RESULTS

After 12 weeks of treatment, mice in the HFHS group had the highest hepatic lipid content. Plasma levels of glucose, insulin, leptin, cholesterol, amylin, and total fat content were significantly elevated in HFHS mice compared to control mice. HFHS feeding increased protein expression of carnitine palmitoyltransferase 1b (CPT-1b isoform) in gastrocnemius, CPT1a, glucose transporter protein 2 (GLUT2), glucocorticoid receptor (GR), and fructose 1,6-bisphosphate 1 (FBP1) expression in liver. Exercise alone had minor effects on these metabolic abnormalities. Genistein alone resulted in improvements in body weight, fat content, amylin, insulin sensitivity, and liver histopathology, GR, FBP1, and acetyl-CoA carboxylase 1 (ACC1). Combination treatment resulted in additional metabolic improvements, including reductions in hepatic lipid content and lipid area, alanine transferase activity, CPT1b, and CPT1a.

CONCLUSION

Our results indicate that a HFHS diet is obesogenic, inducing metabolic perturbations consistent with T2DM and MAFLD. Genistein alone and genistein combined with moderate intensity exercise were effective in reducing MAFLD and the aberrations induced by chronic HFHS feeding.

Association of acrylamide hemoglobin biomarkers with chronic obstructive pulmonary disease in the general population in the US: NHANES 2013-2016

Background: Acrylamide is a well-known potential carcinogenic compound formed as an intermediate in the Maillard reaction during heat treatment, mainly from high-temperature frying, and is found in baked goods and coffee, as well as resulting from water treatment, textiles and paper processing. The effects of acrylamide on lung disease in humans remains unclear. We aimed to investigate the association between blood acrylamide and glycidamide and chronic obstructive pulmonary disease (COPD) in the United States of America (U.S.) population using PROC logistic regression models. Results: 2744 participants aged 20 to 80 from the 2013-2016 National Health and Nutrition Examination Survey (NHANES) were enrolled. After adjusting for demographic data, health factors and serum cotinine, the ratio of HbGA to HbAA (HbGA/HbAA) significantly increased the risk of COPD (P for trend = 0.022). The odds ratio (OR) with a 95% confidence interval (95% CI) for HbGA/HbAA in the third tile was 2.45 (1.12-5.31), compared with the lowest tile. The restricted cubic spline (RCS) curve showed a positive linear correlation between the log (HbGA/HbAA) and the risk of COPD (P = 0.030). Conclusion: The ratio of glycidamide and acrylamide (HbGA/HbAA) was associated with COPD. This association was more prominent in males, obese individuals, people with a poverty income ratio (PIR) < 1.85 or people who never exercise. However, null associations were observed between HbAA, HbGA and HbAA + HbGA, and COPD.

The Influence of Epigenetic Modifications on Metabolic Changes in White Adipose Tissue and Liver and Their Potential Impact in Exercise

Background: Epigenetic marks are responsive to a wide variety of environmental stimuli and serve as important mediators for gene transcription. A number of chromatin modifying enzymes orchestrate epigenetic responses to environmental stimuli, with a growing body of research examining how changes in metabolic substrates or co-factors alter epigenetic modifications.

Scope of Review: Here, we provide a systematic review of existing evidence of metabolism-related epigenetic changes in white adipose tissue (WAT) and the liver and generate secondary hypotheses on how exercise may impact metabolism-related epigenetic marks in these tissues.

Major Conclusions: Epigenetic changes contribute to the complex transcriptional responses associated with WAT lipolysis, hepatic de novo lipogenesis, and hepatic gluconeogenesis. While these metabolic responses may hypothetically be altered with acute and chronic exercise, direct testing is needed.

Effect of Silymarin Supplementation in Lung and Liver Histological Modifications during Exercise Training in a Rodent Model

BACKGROUND

Exercise training induces adaptive physiological and morphological modifications in the entire organism; however, excessive loads of training may increase damage in tissues. The purpose of this study was to evaluate the effect of silymarin in lung and liver histological changes in rats subjected to exercise training (ET).

METHODS

Male Wistar rats were subjected to an 8-week ET treadmill program 5 days per week, 60 min/session, and were previously administered 100 mg ascorbic acid or 100 mg of silymarin.

RESULTS

Silymarin increased alveolar and bronchial muscle size, improve vascularization, and reduced tissue inflammation. In liver, silymarin promoted the reduction of lipid content.

CONCLUSION

Silymarin supplementation may improve inflammation in pulmonary tissue after 8 weeks of the ET treadmill program, improve cell recovery, and reduce intrahepatic lipid content.

Can Resistance Exercise Be a Tool for Healthy Aging in Post-Menopausal Women with Type 1 Diabetes?

Due to improvements in diabetes care, people with type 1 diabetes (T1D) are living longer. Studies show that post-menopausal T1D women have a substantially elevated cardiovascular risk compared to those without T1D. As T1D may also accelerate age-related bone and muscle loss, the risk of frailty may be considerable for T1D women. Exercise and physical activity may be optimal preventative therapies to maintain health and prevent complications in this population: They are associated with improvements in, or maintenance of, cardiovascular health, bone mineral density, and muscle mass in older adults. Resistance exercise, in particular, may provide important protection against age-related frailty, due to its specific effects on bone and muscle. Fear of hypoglycemia can be a barrier to exercise in those with T1D, and resistance exercise may cause less hypoglycemia than aerobic exercise. There are currently no exercise studies involving older, post-menopausal women with T1D. As such, it is unknown whether current guidelines for insulin adjustment/carbohydrate intake for activity are appropriate for this population. This review focuses on existing knowledge about exercise in older adults and considers potential future directions around resistance exercise as a therapeutic intervention for post-menopausal T1D women.